Supported, Bimetallic Nanoparticles for Selective Catalysis

Description:
 

Reference #: 01131

The University of South Carolina is offering licensing opportunities for a bimetallic catalyst system that resists gold agglomeration (common with current carbon-supported gold catalysts) by combining a high surface free energy core metal with a controlled-thickness gold shell structure.

Invention Description:

The subject invention is a method of depositing gold (Au) nanoparticles on top of a series of pre-selected core metals to form a core-metal structure that is resistant to agglomeration.

Potential Applications:

·    Hydrochlorination of acetylene to form vinyl chloride monomer for use in PVC: These supported, core-shell bimetallic nanoparticles use high free energy cores, creating high-stability Au catalysts with the surface area necessary for selective hydrochlorination of acetylene. They can also be utilized in any Au catalyzed chemical reactions, particularly those where Au is not consumed by the reaction

·      Reduction of SO3 to SO2: This system may also be utilized in the reduction of sulfur trioxide (SO3) to form sulfur dioxide (SO2) when splitting water to form H2 and O2. Currently, supported platinum (Pt) catalysts at high temperatures of 600 – 900°C are used to catalyze this reduction. The active Pt catalyst undergoes rapid sintering at these temperatures and catalyst activity declines rapidly, making it an economically unattractive process.

·    Dry reforming of methane (DRM): The supported, bimetallic catalyst system can be used in dry reforming biogas, which contains large quantities of methane and carbon dioxide. Since the DRM process is endothermic and requires a heat energy of 261 kJ/mole, a suitable catalyst is necessary in order for the reaction to proceed at high temperatures. The major obstacles for current catalysts are carbon deposition, particle sintering, and sulfur poisoning.

Advantages and Benefits:

1. The deposited metal forms a controlled and variable-thickness shell on the surface of the pre-selected core metal.

2.  The shell metal remains both resistant to agglomeration on the surface of the support and positioned on the core metal. Therefore, the catalyst system maintains its high catalytic activity.

3. Metal-metal interactions of bimetallic core-shell particles provide a superior method to maintain catalytic surfaces from sintering.

Background:

Polyvinyl chloride (PVC) is the third highest volume plastic after polyethylene and polypropylene. It is produced by polymerization of the vinyl chloride monomer (VCM) which is manufactured in one of two ways: 1) by an oxychlorination method, which generates the majority of VCM, although this route is multi-step, non-selective, and energy intensive, or 2) by direct hydrochlorination of acetylene which is simple and very selective (>99%), although HgCl2/C, the catalyst currently used, undergoes reduction to Hg metal after a short period of time and is volatilized into the environment. In areas where coal is plentiful, the formation of acetylene from coke (CaC2 + H2O reaction) is well-developed technology. Thus, it is necessary to develop more environmentally friendly catalysts for acetylene hydrochlorination.

Carbon-supported Au catalysts have been found to be active and selective catalysts for this reaction. Supported Au catalysts show high activity and selectivity for hydrochlorination of acetylene to vinyl chloride formation. Unfortunately, in the presence of HCl (one of the two reactants), Au particles undergo rapid agglomeration from approximately 2 nm in diameter to form Au particles in excess of 20 nm in diameter. This loss of Au surface sites greatly limits catalytic activity, making this catalyst and process much less attractive.

 

If the Au can be deposited as a controlled-thickness layer on top of another core metal (with surface free energy higher than that of Au), the Au shell should remain resistant to agglomeration and remain on the metal core. This would maintain the high catalytic activity for hydrochlorination and make this process much more economically attractive. Currently, there are no Au-based catalysts for acetylene hydrochlorination on the market.

Experimental Validation:

The core-metal structure remained resistant to agglomeration through 20 hours of testing under harsh conditions. The powder x-ray diffraction pattern of the catalyst after 20 hours on stream was similar to that of the fresh catalyst; specifically, the FCC metal peaks had not sharpened and the estimated particles sizes were as small as the fresh sample.  This analysis confirms that supported Au shells are stable in the reaction environment.

Patent Information:
For Information, Contact:
Technology Commercialization
University of South Carolina
technology@sc.edu
Inventors:
John Monnier
J.r. Regalbuto
Kerry O'connell
Keywords:
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